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SP6690 Evaluation Board Manual
Ideal for series white LED driver High output voltage, up to 30V Low quiescent current: 20uA Ultra low shutdown current: 10nA High Efficiency: up to 80% SOT23-5 Package & SMT components for small, low profile Power Supply
DESCRIPTION AND BOARD SCHEMATIC The SP6690 Evaluation Board is designed to help the user evaluate the performance of the SP6690 as a series white LED driver. The evaluation board is a completely assembled and tested surface mount board which provides easy probe access points to all SP6690 Inputs and Outputs so that the user can quickly connect and measure electrical characteristics and waveforms.
USING THE EVALUATION BOARD 1) Powering Up the SP6690 Circuit The SP6690 Evaluation Board can be powered from inputs from a +1.2V to +5.0V. Connect with short leads directly to the "VIN" and "GND" posts. Monitor the Output Voltage and connect the Load between the "VOUT" post and the "GND" post. 2) Using the J1 Jumper: Enabling the SP6690 Output and using the Shutdown Mode The SP6690 output will be enabled if the J1 Jumper is in the bottom or pin 1 to 2 position. If J1 is in the pin 2 to 3 or top position, the Shutdown pin is brought to GND, which puts the SP6690 in the low quiescent Shutdown Mode. 3) Using the Posts Since the part might get damaged when the output is open loop, two divider resistors (R1=1M, R2=64.9K) are used to provide the feedback loop and set the output voltage. For the white LEDs application, these two resistors (R1, R2) need to be removed from the evaluation board first to avoid overvoltage and then plug the white LED module between "VOUT" and "FB" posts. The bias resistor Rb should also be installed on the board. 4) Inductor Selection For SP6690, the internal switch will be turned off only after the inductor current reaches the typical dc current limit (ILIM =350mA). However, there is typically propagation delay of 200nS between the time when the current limit is reached and when the switch is actually turned off. During this 200nS delay, the peak inductor current will increase, exceeding the current limit by a small amount. The peak inductor current can be estimated by: V I pk = I LIM + in (max) 200nS L The larger the input voltage and the lower the inductor value, the greater the peak current. In selecting an inductor, the saturation current specified for the inductor needs to be greater than the SP6690 peak current to avoid saturating the inductor, which would result in a loss in efficiency and could damage the inductor. Choosing an inductor with low DCR decreases power losses and increase efficiency. Refer to Table 1 for some suggested low ESR inductors. Table 1. Suggested Low ESR inductor
MANUFACTURE
PART NUMBER LQH32CN100K11 (10uH) NLC453232T-100K (22uH)
DCR () 0.3 0.55
Current Rating (mA) 450 500
MURATA 770-436-1300 TDK 847-803-6100
5) Diode Selection A schottky diode with a low forward drop and fast switching speed is ideally used here to achieve high efficiency. In selecting a Schottky diode, the current rating of the schottky diode should be larger than the peak inductor current. Moreover, the reverse breakdown voltage of the schottky diode should be larger than the output voltage. 6) Capacitor Selection Ceramic capacitors are recommended for their inherently low ESR, which will help produce low peak to peak output ripple, and reduce high frequency spikes. For the typical application, 4.7uF input capacitor and 2.2uF output capacitor are sufficient. The input and output ripple could be further reduced by increasing the value of the input and output capacitors. Place all the capacitors as close to the SP6690 as possible for layout. For use as a voltage source, to reduce the output ripple, a small feedforward (47pF) across the top feedback resistor can be used to provide sufficient overdrive for the error comparator, thus reducing the output ripple. Refer to Table 2 for some suggested low ESR capacitors.
Table 2. Suggested Low ESR capacitor
MANUFACTURE MURATA 770-436-1300 MURATA 770-436-1300 TDK 847-803-6100 TDK 847-803-6100 PART NUMBER GRM32RR71E 225KC01B GRM31CR61A 475KA01B C3225X7R1E 225M C3216X5R1A 475K CAP /VOLTAGE 2.2uF /25V 4.7uF /10V 2.2uF /25V 4.7uF /10V SIZE /TYPE 1210 /X5R 1206 /X5R 1210 /X7R 1206 /X5R
7) LED Current Program In the white LEDs application, the SP6690 is generally programmed as a current source. The bias resistor R b is used to set the operating current of the white LED using the equation: V R b = FB IF where VF B is the feedback pin voltage (1.22V), IF is the operating current of the White LEDs. In order to achieve accurate LED current, 1% precision resistors are recommended. Table 3 below shows the Rb selection for different white LED currents. For example, to set the operating current to be 20mA, Rb is selected as 60.4 Ohm, as shown in the schematic. Table 3. Bias Resistor Selection IF (mA) Rb () 5 243 10 121 12 102 15 80.6 20 60.4 8) Vout Programming The SP6690 can be programmed as either a voltage source or a current source. To program the SP6690 as voltage source, the SP6690 requires 2 feedback resistors R1 & R2 to control the output voltage. The formula for the resistor selection are shown below.
V R 1 = out - 1 * R 2 1.22
9) Open Circuit Protection When any white LED inside the white LED module fails or the LED module is disconnected from the circuit, the output and the feedback control will be open, thus resulting in a high output voltage, which may cause the SW pin voltage to exceed it maximum rating. In this case, a zener diode can be used at the output to limit the voltage on the SW pin and protect the part. The zener voltage should be larger than the maximum forward voltage of the White LED module. 10) Brightness Control Dimming control can be achieved by applying a PWM control signal to the EN/PWM pin. The brightness of the white LEDs is controlled by increasing and decreasing the duty cycle of The PWM signal. A 0% duty cycle corresponds to zero LED current and a 100% duty cycle corresponds to full load current. While the operating frequency range of the PWM control is from 60Hz to 700Hz, the recommended maximum brightness frequency range of the PWM signal is from 60Hz to 200Hz. A repetition rate of at least 60Hz is required to prevent flicker. The magnitude of the PWM signal should be higher than the minimum SHDN voltage high. 11) Layout Consideration Both the input capacitor and the output capacitor should be placed as close as possible to the IC. This can reduce the copper trace resistance which directly effects the input and output ripples. The feedback resistor network should be kept close to the FB pin to minimize copper trace connections that can inject noise into the system. The ground connection for the feedback resistor network should connect directly to the GND pin or to an analog ground plane that is tied directly to the GND pin. The inductor and the schottky diode should be placed as close as possible to the switch pin to minimize the noise coupling to the other circuits, especially the feedback network.
POWER SUPPLY DATA For the standard evaluation board (4x20mA series white LEDs application), in which the output voltage is around 15V and output current is 20mA, the power supply data is provided in Fig 1. to Fig. 4. The white LEDs used here were from LUMEX (Part Number: SML-LX2832UWC-TR).
90
Average Output Current (mA)
20
85 80
16
Efficiency (%)
75 70 65 60 55 50 2.7 3 3.3 3.6 3.9 4.2 Input Voltage (V)
12
8
4
0 0 20 40 60 80 100
PWM Duty Cycle (%)
Fig. 1 Efficiency vs Input Voltage
Fig. 2 Average Io vs SHDN duty cycle
Vsw IL
(0.5A/DIV)
Vout
(AC)
Vout
(AC)
Fig. 3 Typical Switching Waveform (Vin=3.3V)
Fig. 4 Output Ripple (Vin=2.7V)
.
EVALUATION BOARD LAYOUT
FIGURE 1: SP6690EB COMPONENT PLACEMENT
FIGURE 2: SP6690EB PC LAYOUT TOP SIDE
FIGURE 3: SP6690EB PC LAYOUT BOTTOM SIDE
TABLE1: SP6690LEB LIST OF MATERIALS
Ref. Des. SP6690 Evaluation Board List of Materials Qty. Manufacturer Part Number Layout Size Component LxWxH 1 Sipex Corp. 146-6512-00 1"x1.5" SP6690 Eval PC Board 1 Sipex Corp. SP6690EK SOT23-5 5-pin SOT23 Step-Up DC/DC Conv 1 Murata GRM31CR61A475KA01B 1206 Ceramic 10V 4.7uF SM 1 Murata GRM32RR71E225KC01B 1210 Ceramic 25V 2.2uF SM 1 Murata GRM1885C1H470JA01B 603 Ceramic 47pF SM 1 Murata LQH32CN100K11 3.2X2.5X2mm 10uH, 0.45A, 0.3 Ohm, SM Inductor 1 Panasonic ERJ-3EKF1004 603 1M Ohm 1/16W 1% 0603 SM 1 Panasonic ERJ-3EKF6492 603 64.9K Ohm 1/16W 1% 0603 SM 1 Panasonic ERJ-3EKF60R4V 603 Open 1 On-Semi MBR-0530 SOD-123 Schottky Diode 30V, 0.5A 1 SOD-123 Open 5 Mill-Max 0300-115-01-4727100 .042 Dia Test Point Female Pin 1 Sullins PTC36SAAN .23x.12 2-Pin Header Vendor Sipex 978-667-8700 Sipex 978-667-8700 Murata 770-436-1300 Murata 770-436-1300 Murata 770-436-1300 Murata 770-436-1300 800-Digi-Key 800-Digi-Key 800-Digi-Key Onsemi 800-Digi-Key 800-Digi-Key
U1 C1 C2 C3 L1 R1 R2 Rb DS D1-D4 TP J1
ORDERING INFORMATION Model Temperature Range Package Type
SP6690EB............................. -40C to +85C...................SP6690 Evaluation Board SP6690EU.....................................-40C to +85C......................................5-pin SOT-23

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